1. Field of the Invention
The present invention relates to a gear shaper cutting apparatus and method for gear shape cutting with use of gear shaping tools such as a pinion cutter and a rack cutter having a cutting edge portion made of high-speed tool steel.
2. Description of Related Art
FIG. 11 shows a conventional gear shaper apparatus and cutting method (gear shaping method). A work 1 is loaded into a work fixture 3 on a table 2 of a gear shaping machine (hereinafter, referred to as gear shaper). A pinion cutter 4, which is a gear shaping tool, is mounted to a cutter head 5 of the gear shaper. The pinion cutter 4 is made of high-speed tool steel. Cutting (generation) of teeth onto the work 1 is performed by vertically reciprocating the pinion cutter 4 to allow it to cut into the work 1, and further imparting relative rotations to the pinion cutter 4 and the work 1. The teeth are successively formed on the outer peripheral surface of the work 1. The machining conditions are determined so that predetermined teeth are generated on the outer periphery of the work 1. During the machining operation, cutting oil 6 is sprayed onto a cutting portion through a nozzle 7 to lubricate and cool the cutting portion.
Such a conventional gear shaper apparatus and cutting method as mentioned above has had a problem that the gear cutting speed is low, which increases the machining cost. The gear cutting speed is substantially determined by the speed (hereinafter, referred to as cutting speed) of the pinion cutter 4 when vertically moving, which is usually 40 m/min for rough cutting and about 70 m/min for finish cutting.
Also, since cutting oil is sprayed, the working environment worsens, and waste liquor disposal of the cutting oil is required. This has led to a problem wherein cost is also increased for the disposal.
Recently, a high-speed gear shaping cutting technique using a gear shaping tool made of cemented carbide has been developed. Thus, the generation of teeth by a gear shaper has become more efficient. In the case of using a gear shaping tool made of cemented carbide, a heat crack will develop if machining is performed under the supply of cutting oil, because cemented carbide is fragile. For this reason, in the case of using a gear shaping tool made of cemented carbide, a dry cutting method in which machining is performed without the supply of cutting oil is mainly adopted. Since cemented carbide is much higher in both heat resistance and wear resistance than the high-speed tool steel, no problem occurs even if such dry cutting is performed.
As mentioned above, the machining efficiency is improved by using a gear shaping tool made of cemented carbide and it may become possible to reduce the machining cost by the increased cutting speed. However, the gear shaping tool made of cemented carbide is so expensive that the total cost becomes extremely high even if the machining efficiency is improved. In addition, since cemented carbide is fragile, there is a fear that a sudden crack may occur. For this reason, the gear shaping tool of cemented carbide is not presently in wide practical use.